X-ray binaries

Sergei Popov (SAI MSU)

Picture: V.M.Lipunov

Wealth of observational manifestations:

Visual binaries orbits, masses

Close binaries effects of mass transfer

Binaries with compact stars

X-ray binaries, X-ray transients, cataclysmic variables, binary pulsars,black hole candidates, microquasars…

Binaries are important and different!

Beta Lyra’s portrait

[M. Zhao et al.] arXiv:0808.0932

CHARA ArraySix 1-meter telescope form an interferrometer with basesfrom ~30 to ~300 meters.

We see a donor-star and a discaround the second star.

DIrect measurement of the distance

The most massive binary

[Schnurr et al. arxiv:0806.2815]

NGC3603-A1

116+/-31 M0

89+/-16 M0

3.77-day double-eclipsing binary

Algol (β Per) paradox: late-type (lighter) component is at more advanced evolutionary stage than the early-type (heavier) one!

Key to a solution: component mass reversal due tomass transfer at earlier stages!

0.8 M G5IV 3.7 B8 V

Algol paradox

Roche lobes and Lagrange points

Three-dimensional representation of the gravitational potentialof a binary star (in a corotating frame) and several cross sections of theequipotential surfaces by the orbital plane. The Roche lobe is shown by thethick line

GS 2000+25 and Nova Oph 1997

(Psaltis astro-ph/0410536)

On the left – Hα spectrum,On the right – the Dopler image

See a review in Harlaftis 2001(astro-ph/0012513)

GS 2000+25

Nova Oph 1997

There are eclipse mapping, dopller tomography (shown in the figure), and echo tomography (see 0709.3500).

Models for the XRB structure

(astro-ph/0012513)

Evolution of normal stars

Evolutionary tracks of single stars with masses from 0.8 to 150M. The slowest evolution is in the hatched regions(Lejeune T, Schaerer D Astron. Astrophys. 366 538 (2001))

A track for a normal 5 solar mass star

Progenitors and descendants

Descendants of components of close binaries depending on the radius of the star at RLOF.

The boundary between progenitors of He and CO-WDs is uncertain by several 0.1MO.The boundary between WDs and NSs by ~ 1MO, while for the formation of BHs the lower mass limit may be even by ~ 10MO higher than indicated.

[Postnov, Yungelson 2007]

Mass loss depends on which stage of evolution the star fills its Roche lobe

If star is isentropic (e.g. deep convective envelope - RG stage), mass loss tends to increase R with decreasing M which generally leads tounstable mass transfer.

Mass loss and evolution

Three cases of mass transfer lossby the primary star(after R.Kippenhahn)

In the most important case Bmass transfer occurs onthermal time scale:

dM/dt~M/τKH , τKH=GM2/RL

In case A: on nuclear timescale: dM/dt~M/tnuc

tnuc ~ 1/M2

Different cases for Roche lobe overflow

Close binaries with accreting compact objects

Among binaries ~ 40% are close and ~96% are low and intermediate mass ones.

LMXBsRoche lobe overflow.Very compact systems.Rapid NS rotation.Produce mPSRs.

IMXBsVery rare.Roche lobe overflow.Produce LMXBs(?)

HMXBsAccretion from the stellar wind.Mainly Be/X-ray.Wide systems.Long NS spin periods.Produce DNS.

Intermediate mass X-ray binaries

(Podsiadlowski et al., ApJ 2002)

Most of the evolution time systems spend as an X-ray binary occurs after the mass of the donor star has been reduced to <1MO

Otherwise, more massivesystems experiencing dynamical mass transfer and spiral-in.

IMXBs and LMXBs population synthesis

(Pfahl et al. 2003 ApJ)

Low mass X-ray binaries

NSs as accretorsX-ray pulsarsMillisecond X-ray pulsarsBurstersAtoll sourcesZ-type sources

WDs as accretorsCataclismic variables• Novae• Dwarf novae• Polars• Intermediate polarsSupersoft sources (SSS)

BHs as accretorsX-ray novaeMicroquasarsMassive X-ray binaries

LMXBs with NSs or BHs

The latest large catalogue (Li et al. arXiv: 0707.0544) includes 187 galacticand Magellanic Clouds LMXBs with NSs and BHs as accreting components.Donors can be WDs, or normal low-mass stars (main sequence or sub-giants).Many sources are found in globular clusters.Also there are more and more LMXBs found in more distant galaxies.

In optics the emission is dominated by an accretion disc around a compact object.Clear classifiction is based on optical data or on mass function derived from X-ray observations.If a source is unidentified in optics, but exhibits Type I X-ray bursts, or just has a small (<0.5 days) orbital period, then it can be clasified as a LMXB with a NS.In addition, spectral similarities with known LMXBs can result in classification.

Evolution of low-mass systems

A small part of the evolutionary scenario of close binary systems

[Yungelson L R, in Interacting Binaries: Accretion, Evolution, Out-Comes 2005]

Evolution of close binaries

(Postnov, Yungelson 2007)

Van den Heuvel, Heise 1972

First evolutionary “scenario” for the formation of X-ray binary pulsar

Non-conservative evolution:Common envelope stage (B.Paczynski, 1976)

Problem: How to make close binarieswith compact stars (CVs, XRBs)?Most angular momentum from the system should be lost.

Common envelope

Tidal effects on the orbit (Zahn, 1977)

1. Circularization

2. Synchronization of component’s rotation

Both occur on a much shorter timescale than stellar evolution!

Conservative mass transfer

1 2

1 2

' '1 1 2 2

2 12 1

2 11 2

M=M M

Assuming (B.Paczynski):

Change of orbital parameters after mass transfer:

, ,

0, if > 2

0, if

orb

const

M MJ aM const

M

M M M M M M

M Ma M MM

M Ma M M

Non-conservative evolution

Massive binaries: stellar wind, supernova explosions, common envelops

Low-massive binaries: common envelops, magnetic stellar winds, gravitational wave emission (CVs, LMXBs)

Stellar captures in dense clusters (LMXBs, millisecond pulsars)

Formation of close low-massbinaries is favored in dense stellar systems due to various dynamical processes

Hundreds close XRB and millisecondpulsars are found in globular clusters

Binaries in globular clusters

Isotropic wind mass loss Effective for massive early-type stars on main

sequence or WR-stars Assuming the wind carrying out specific orbital

angular momentum yields:

a(M1+M2)=const

Δa/a=-ΔM/M > 0

The orbit always gets wider!

Supernova explosion

First SN in a close binary occurs in almost circular orbit ΔM=M1 – Mc , Mc is the mass of compact remnant

Assume SN to be instantaneous and symmetric

1

1 2

2

2

Energy-momentum conservation

2f

i c

c

a M M

a M M

MeM M

If more than half of the total mass is lost, the system becomes unbound

BUT: Strong complication and uncertainty: Kick velocities of NS!

• Magnetic stellar wind.Effective for main sequence stars with convective envelopes 0.3<M<1.5 M

• Gravitational radiation.Drives evolution of binaries with P<15 hrs

Especially importantfor evolution of low-massclose binaries!

Angular momentum loss

Mass loss due to MSW and GW

MSW is more effective at larger orbital periods, but GW always wins at shorterperiods! Moreover, MSWstops when M2 ~0.3-0.4 M

where star becomes fullyconvective and dynamo switches off.

P

GW~a-4

MSW~a-1

dL/dt

1/ 2

2 2

Axial rotation braking of single G-dwarfs (Skumanich, 1972)

~ , where is the age

: stellar wind plasma ``streams'' along magnetic field lines

until v ~ ( ) / 4 , so carries away muc

Physics

V t t

B r

2

2

h larger specific

angular momentum (Mestel).

Assume the secondary star in a low-mass binary

(0.4 M 1.5 ) experiences m.s.w. Tidal forces tend

to keep the star in corotation with orbital revolution:

M

2

2

4 22

51

.

Angular momentum conservation then leads to:

Recolling that: and using Kepler's 3d law we get

ln~

orb

orb

orb

dL dJ

dt dt

L a

d L R GM

dt M a

Binary evolution: Major uncertainties All uncertainties in stellar evolution (convection treatment, rotation, magnetic

fields…) Limitations of the Roche approximation (synchronous rotation, central

density concentration, orbital circularity) Non-conservative evolution (stellar winds, common envelope treatment,

magnetic braking…) For binaries with NS (and probably BH): effects of supernova asymmetry

(natal kicks of compact objects), rotational evolution of magnetized compact stars (WD, NS)

NS Masses

We know several candidates to NS with high masses (M>1.8 Msun):

Vela X-1, M=1.88±0.13 or 2.27±0.17 Msun (Quaintrell et al., 2003) 4U 1700-37, M=2.4±0.3 Msun (Clark et al., 2002) 2S 0921-630/V395 Car, M=2.0-4.3 Msun [1] (Shahbaz et al., 2004) J0751+1807, M=2.1+0.4/-0.5Msun(Nice,Splaver,2004) binary radiopulsar!

In 1999 Ouyed and Butler discussed an EOS based on the model by (Skyrme 1962). A NS with such EOS has Mmax=2.95Msun for a non-rotating configuration and Mmax=3.45Msun for extreme rotation. This model defines the upper mass limit for our study.

We will discuss formation of very massive NS due to accretion processes in binary systems.

What is «Very Massive NS» ?

1.8 Msun < Very Massive NS < 3.5 Msun

• 1.8Msun: (or ~2Msun) Upper limit of Fe-core/young NS according to modeling of Supernova explosions (Woosley et al. 2002).

• ~3.5Msun: Upper limit of rapidly rotating NS with Skyrme EOS (Ouyed 2004).

Evolution

For our calculations we use the “Scenario Machine’’ code developed at the SAI. Description of most of parameters of the code can be found in (Lipunov,Postnov,Prokhorov 1996)

Results

1 000 000 binaries was calculated in every Population Synthesis set

104 very massive NS in the Galaxy (formation rate ~6.7 10-7 1/yr) in the model with kick

[6 104 stars and the corresponding formation rate ~4 10-6 1/yr for the zero kick].

State of NS with kick zero kick

Ejector 32% 39%

Propeller+Georotator 2% 8%

Accretor 66% 53%

astro-ph/0412327

Results II

Mass distribution of very massive NS

Dashed line: Zero natal kick of NS ( just for illustration).Solid line: Bimodal kick similar to (Arzoumanian et al. 2002).

Luminosity distribution of accreting very massive

NS

Extragalactic binariesIt is possbile to study galactic-like binaries up to 20-30 Mpc.For example, in NGC 4697 80 sources are known thanks to Chandra(this is an early type galaxy, so most of the sources are LMXBs).

LMXBs luminosity function

LMXB galactic luminosity function (Grimm et al. 2002)

LMXB luminosity function for NGC 1316(Kim and Fabbiano 2003)

LMXBs luminosity function

(see Fabbianno astro-ph/0511481)

Cumulated XLF for 14 early-type galaxies.

List of reviews• Catalogue of LMXBs. Li et al. arXiv:0707.0544 • Catalogue of HMXBs. Li et al. arXiv: 0707.0549• Evolution of binaries. Postnov & Yungelson. astro-ph/0701059• Extragalactic XRBs. Fabbiano. astro-ph/0511481• General review on accreting NSs and BHs. Psaltis. astro-ph/0410536 • CVs- Evolution. Ritter. arXiv:0809.1800- General features. Smith. astro-ph/0701564• Modeling accretion: Done et al. arXiv:0708.0148• X-ray Properties of Black-Hole Binaries. Remillard & McClintock, astro-ph/0606352• Models for microquasars spectra. Malzac. arxiv:0706.2389• X-ray observations of ultraluminous X-ray sources. Roberts. arxiv:0706.2562• Population synthesis. Popov & Prokhorov. Physics Uspekhi (2007)